1. Field of the Invention
The present invention relates to an extracting device for extracting a specific area within a fingerprint image that is suitable for fingerprint collation, to an evaluation apparatus for evaluating the quality of the fingerprint image based on the aforementioned area, and to a fingerprint collation apparatus.
2. Description of the Related Art
In general, a fingerprint constituted with a great number of ridgelines in striped patterns has two significant characteristics that it does not change throughout one's life and that no one has the same pattern. Therefore, fingerprints have been used for a long time as a way of verifying individuals.
Recently, various countries such as the United States have started to employ identity confirmation using the fingerprint, as a method for enabling a strict immigration control. Further, fingerprint collation as the identity recognition, which is performed at the time of entering/leaving a gate or at the time of log-in, has also become widespread.
In such operations, it is important to judge the quality of an input fingerprint automatically. If it is possible to judge that the fingerprint quality is bad, the fingerprint can be rejected and re-input can be requested. Thus, it becomes possible to deal with such case operationally.
As a method for judging the quality of the fingerprint image, conventionally, there is a method for judging the quality based on whether the direction of the ridgelines of the fingerprint is detected or not and the reliability of that detection, as disclosed in Japanese Unexamined Patent Publication 2002-32757 (Patent Literature 1) and Japanese Unexamined Patent Publication 2003-337949 (Patent Literature 2). In addition, also widely used is a method which judges the quality by using an area where the ridgeline direction can be recognized, as disclosed in U.S. Pat. No. 5,963,656 (Patent Literature 3).
In the above-described techniques, however, the common area in the two fingerprints to be verified is not considered. Thus, when judged that the similarity therebetween is low because of narrow common area, it is necessary to apply improvements so that the judgment can be executed accurately. For example, two fingerprints shown in FIG. 12A and FIG. 12B are the same fingerprints. The fingertip part above the center point of the fingerprint is impressed in FIG. 12A, whereas the area including the center point of the fingerprint is impressed in FIG. 12B. Since the common areas of the two fingerprints, i.e. the areas that overlap with each other at the center points of the two fingerprints, are narrow, it is highly possible that the collation turns out as a failure. However, looking at the two fingerprints individually, the ridgeline directions of each fingerprint are clear and the impressed areas of the two fingerprints are not narrow. Therefore, with the above-described method, it is possible that the qualities of the both fingerprints are judged as being high qualities. From the view point of judging the degree of the similarity between the fingerprints, this needs to be improved.
In order to guarantee the common areas of the fingerprint images as the collation targets, there is proposed a technique that is disclosed in U.S. Pat. No. 6,005,963 (Patent Literature 4). This technique judges whether or not the fingerprint image is a partial impression and, when it is a partial impression, rejects the collation and encourages a re-input, etc. As a method for judging it as a partial image, this technique judges whether or not a ridge trace line that surrounds the image center is sufficiently extended in a left downward direction and right downward direction. However, even if the method is capable of judging the partial fingerprint that is missing the left area or the right area, it is not capable of judging the partial fingerprint that is missing the top area or the bottom area. Thus, in the case of FIG. 12, it is judged even using this method that both fingerprints are not the partial fingerprints and both are of the high quality. Therefore, the aforementioned issue cannot be overcome with this technique.
Further, in order to perform the fingerprint collation with high accuracy, it is preferable for the common areas of a plurality of fingerprint images as the collation targets to include the part where the features of the fingerprints appear prominently, i.e. the center part of so-called a whorl. Thus, there has been desired a technique for evaluating the fingerprint quality, which is capable of judging the fingerprint image including such part as being a high-quality image.
Meanwhile, the mainstream of the collation of fingerprints is a collation of the minutiae, with which the minutiae of the fingerprints such as the end points or bifurcations of the ridgelines are extracted, and collation is performed by using the minutiae. However, there is a limit in the accuracy of the collation that is performed only with the minutiae. Thus, it has been desired to improve the accuracy of the fingerprint collation by defining a new feature quantity to be used for collation. Further, a collation device by using new data is also desired to take the place of the collation performed by the minutiae of the ridgelines.
The foregoing issues can be overcome if a specific area including a characteristic part of the inherent pattern of individual fingerprint can be extracted from an inputted fingerprint image of a human being or other creature. It is because fingerprint quality judgment and fingerprint collation with high accuracy can be achieved by utilizing information regarding: whether or not extraction can be performed perfectly; degree of extraction such as whether or not the partial extraction is performed; position, range and the like of the extracted area. However, conventionally, there has been no such technique for recognizing and extracting such specific area.